At the heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk rotates, air adjacent to the disk surface moves with it. This allows the slider to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Typically magnetic disk drives have been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Data density requirements are fast approaching the physical limits, however. For example, increased data capacity requires decreased bit sizes, which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write head technologies is reaching its physical limit.
One means for overcoming this physical limit has been to introduce perpendicular recording. In a perpendicular recording system, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. This flux then flows through the relatively magnetically soft underlayer and returns to the surface of the disk at a location adjacent a return pole of the write element. The return pole of the write element has a cross section that is much larger than that of the write pole so that the flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the flux too week to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.
Efforts to minimize track width and bit size when using perpendicular recording have focused on the formation of the write pole since the write pole defines both the track width and the bit size. Most desirably, the write pole should have a trapezoidal, or tapered shape in order to prevent adjacent track writing problems associated with skew. As those skilled in the art will recognize, skew occurs as an actuator arm swings the magnetic head to either extreme of its pivot range (ie. at the inner and outer portions of the disk). Such skew positions the head at an angle, which positions portions of the write pole outside of the desired track. Forming the write pole with a trapezoidal shape reduces such adjacent track writing.
Another attempt to improve write pole performance has focused on reducing remnance. Remnance is the slower than desired magnetization decay when the write current is turned off. Because a large amount of flux is being forced into a relatively small write pole, when the write current is turned off the magnetization of the write pole does not immediately cease, but continues for an undesirably long period of time. An approach to alleviate this has been to form the write pole as laminations of magnetic layers having very thin layers of non-magnetic material disposed therebetween.
Efforts to form the desired trapezoidal, laminated write poles have involved forming laminated layers of high Bsat magnetic material and then depositing a hard mask and a photoresist patterning mask. A material removal process such as reactive ion etch (RIE) has then been used, with the photoresist as a mask, to pattern the hard mask. Ion milling has then been used to remove the magnetic material there under. An angled ion milling process has then been used to form the desired tapered shape of the write pole.
A problem that has been encountered with the above, however, is that due to poor RIE selectivity between the hard mask and the photoresist mask layer, the photoresist mask layer must be made very thick. This is because a large amount of the photoresist must be consumed in the patterning of the hard mask. As increased data densities require smaller track widths, the tall photoresist structure becomes problematic. For example it would be desirable to use deep ultraviolet (deep U.V.) photolithography or e-beam photolithography, because these processes provide high resolution and allow a well defined small track width write pole to be constructed. However, in general, thicker resist degrades resolution due to worsening aerial imaging in the case of deep UV lithography, and increased blurring due to forward scattering in the case of e-beam lithography. In addition, since the aspect ratio (height to width) of a photoresist mask is limited by physical capabilities of the material, as track widths decrease the thickness must likewise decrease.
In addition, with the ever increasing need to increase data density and write speed, researchers have worked to develop magnetic writers that can avoid adjacent track writing and increase magnetic switching speed. One way to do this is to produces a write head with a trailing shield or a wrap around trailing shield. A trailing shield increases write speed by canting the magnetic field slightly away from vertical. This decrease the switching field, decreasing the time and field needed to switch the magnetic state of the writer from one state (ie into the medium) to the other state (ie. out of the medium). A wrap around shield provides a further advantage in that the shield absorbs stray magnetic fields, either from the write pole or from other write head structures, thereby preventing adjacent track writing. This is especially advantageous when the density of write tracks is increased to increase data density. However, the spacing between the trailing edge of the write pole and the trailing shield (trailing shield gap) is very critical in such a design. If the spacing is too small, write field will be lost to the shield, and if the spacing is too large, the write field will not be canted and the effectiveness of the trailing shield will be lost.
As the tracks of data are spaced closer together to provide increased data density, the track width must be very tightly controlled. Since the track width of the writer is defined by the write pole, the width of the write pole, especially at the trailing edge must be carefully controlled. In addition for write pole with trailing or a wrap around shield, the trailing edge must be clear and planar. Current masking and milling operations used to construct a write head consume an undesirable amount of the mask structure and sides of the write pole material and provide some inconsistency in track width definition.
Therefore, there is a need for a process for forming a write pole of a perpendicular write head that is compatible with the need to construct a trailing or a wrap around shield. Such a process would preferably allow for tight control of a gap thickness between the trailing edge of the write pole and the trailing shield. Such a process would also preferably be useful in constructing a write pole having a desired shape and having a very well controlled track width at the trailing edge of the write pole.